As soon as the arterial line is inserted in the operating room for monitoring purposes, 10mL of blood will be collected for measuring plasma ropivacaine levels. This measurement will be repeated on arrival in the PACU along with routine postoperative arterial blood gas analysis. Plasma ropivacaine level will be measured on postoperative day 1 at 6AM with the blood drawn along with routine postoperative blood work (venous sample)